Numerous chemical investigations have resulted in alternative methods to recover copper from both acid and ammoniacal solutions. Among those which are pertinent to the present invention are:
A. A process (U.S. Pat. No. 723,949) described by George D. van Arsdale which consists of saturating copper sulfate solutions with sulfur dioxide and submitting these solutions to the action of heat and pressure to partially precipitate the copper content and form a proportional amount of sulfuric acid. PA1 B. A process (German Pat. No. 189,974) described by Lucian Jumau which consists of precipitating copper sulfite and decomposing it with sulfuric acid. Also, a process (German Pat. No. 204,673) described by Lucian Jumau in which copper sulfite is treated with water in an autoclave at temperatures from 140.degree. to 170.degree. Centigrade. PA1 C. A process (U.S. Pat. Nos. 3,148,051 and 3,228,765) described by Estanislao J. Chupungco, et al., which consists of treating copper ammine solutions with sulfur dioxide to precipitate a copper ammonium sulfite which is subsequently treated with sulfuric acid or oxygen to obtain metallic copper, copper sulfate, and/or copper oxide together with ammonium sulfate and sulfur dioxide.
It should be pointed out that, although the majority of these processes were developed some time ago, they have not been applied commercially due to the low efficiency with which metallic copper is produced. None of these processes lead to recovery, as metallic copper, or more than about 50% to 80% of the copper content of the copper sulfite (or sulfate). Thus, they are characterized by costly and difficult recirculation of copper sulfate solutions or treatment of other copper components produced. For example, the efficiency in converting copper sulfite to metallic copper using sulfuric acid (Jumau Process) varies from 33% to 40%, the efficiency in converting copper sulfite to metallic copper using heat and pressure (Jumau Revised Process) is between 70 and 75%, the efficiency in converting copper sulfate to metallic copper (van Arsdale Process) is between 50% and 60%, and the efficiency of the conversion of copper ammonium sulfite to metallic copper (E. J. Chupungco Process) with sulfuric acid is from 50% to 60% and with oxygen is from 30% to 40%.